1. Field of the Invention
The present invention relates to a fastening structure, which can fasten a bicycle stem to a bicycle front fork.
2. Description of the Prior Art
Please refer to FIG. 1. The inner hole (11) of the bicycle stem (10) is used for a front fork inserting therein, so that the bottom of the stem (10) abuts against the rib ring (21) of the front fork (20), and the top of the stem (10) protrudes from the front fork (20). The front fork (20) which has a middle hole (22) can be fixed to the stem (10) with a fastening structure.
The fastening structure comprises a cap (30), a bolt (40), a nut (50) and a packing ring (60). The cap has a pillar (31) corresponding to the top edge of the middle hole (22) of the front fork (20), a ring shoulder (32) abutting against the top end of the stem (10), and a head hole (33) passing though the cap (30). The bolt (40) has a bolt head (41) corresponding to the head hole (33), a bolt rod (42) penetrating into the middle hole (22) of the front fork (20). The nut (50) is located in the middle hole (22) of the front fork (20), and its top edge is formed with a shoulder portion (51). A through threaded hole (52) is formed in a central position of the nut (50). The packing ring (60) is adapted for the bolt rod (42) penetrating therethrough, so the packing ring (60) is limited between the cap (30) and the nut (50). The packing ring (60) has a circle portion (61) which can be positioned to the shoulder portion (51). Two opposite sides of the circle portion (61) extends upward to form two bottom cone portions (62), and an interval between the two bottom cone portions (62) is gradually enlarged from the circle portion (61). A top end of each bottom cone portion (62) extends upward so as to form a positioning portion (63), and an interval between the two positioning portions (63) is constant. A top end of each positioning portions (63) extends upward so as to form a top cone portion (64), and an interval between the two top cone portions (64) is gradually contracted from the two positioning portion (63), so that a top end of each top cone portion abuts against a bottom of the cap (30).
Thereby, when screwing the bolt (40) to drive the nut (50) to move toward the cap (30), the nut (50) can press against the packing ring (60) so as to make the positioning portion (63) expand outwards to tightly fit the middle hole (22) of the front fork (20). Consequently, the stem (10) can be fastened to the front fork (20).
However, said fastening structure has the following disadvantages. At first, it comprises too many components, so the production cost is high. In addition, the nut (50) and the packing ring (60) are separated components instead of a modular component which can be formed as one unit. As a result, it is inefficient to assemble the nut (50) and the packing ring (60), and those components are prone to be lost when disassembling the structure. Further, when screwing the bolt, the packing ring (60) may rotate with respect to the nut (50), so that positioning portion (43) may fail to tightly fit the middle hole (22) of the front fork (20).
The present invention is, therefore, arisen to obviate or at least mitigate the above mentioned disadvantages.